1. Field of the Invention
The present invention relates to an automatic feeding device that feeds recording medium one by one from the plural sheets thereof stacked thereon. The invention also relates to a recording apparatus provided with such automatic feeding device.
2. Related Background Art
A recording apparatus provided with an automatic feeding device performs the skew (diagonal conveyance) preventing operation, which adjusts the advancing direction of a sheet by enabling the tip of the sheet to abut against the nipping portion formed by a sheet feeding roller and a pinch roller facing it, before the recording sheet (recording medium) thus fed arrives at a recording area.
In the structure where the sheet feeding roller of a recording apparatus and an automatic feeding device are driven by use of one and the same driving source, there often adopted a structure in which a planetary arm and a planetary gear are used for switching the driving transmissions of the sheet feeding roller in order to prevent the automatic feeding device from being operated during a recording operation.
FIGS. 16A to 16D are views that schematically illustrate the skew preventing operation of the conventional automatic feeding device.
As shown in FIG. 16A, the driving gear 135, which is provided for a driving source (not shown), drives a sheet feeding roller gear 136 directly. Then, up to a sheet feeding shaft gear 119, the driving power is transmitted through an idler gear 137, a sun gear 138, and a planetary gear 139. A planetary arm 140 supports the sun gear 138 and the planetary gear 139 so as to provide the planetary gear 139 with resistance. Also, on a sheet feeding tray 116, recording sheets are stacked.
When the sheet feeding operation begins by use of a driving source (not shown), the driving gear 135 rotates in the direction indicated by an arrow P shown in FIG. 16B. Then, the sheet conveying roller 130, the idler gear 137, and the sun gear 138 rotate in the directions indicated by the respective arrows. At this juncture, for the planetary arm 140, the rotational momentum occurs in the direction indicated by an arrow Q in FIG. 16B. As a result, the planetary gear 139 is connected with the sheet-feeding shaft gear 119 to enable the sheet-feeding roller (not shown) to rotate in the direction indicated by an arrow R in FIG. 16B. At this juncture, the sheet-feeding roller and the separation roller 112, which abuts against thereto, separates and feeds the recording sheet 120 one by one.
In this state, the sheet-conveying roller 130 rotates in the direction in which the recording sheet 120 is conveyed reversely, and the sheet-feeding roller (not shown), which is connected with the sheet-feeding shaft gear 119, is caused to rotate in the direction in which the recording sheet 120 is conveyed to the recording area.
When the conveyance of the recording sheet 120 continues as it is, the leading end of the recording sheet 120 arrives at the nipping portion formed by the sheet conveying roller 130 and the pinch roller 129.
Here, the conveyance of the recording sheet 120 continues for a designated amount, and then, as shown in FIG. 16C, the leading end of the recording sheet 120 abuts against the sheet conveying roller 130 that rotates in the reverse-conveyance direction, thus forming a bend (loop) for the recording sheet 120. In this way, even if the recording sheet 120 is conveyed diagonally up to that point, it is possible to the leading end of the recording sheet 120 is placed along the nipping portion of the sheet conveying roller 130 and the pinch roller 129 to correct the advancing direction of the recording sheet 120, hence preventing the skew of the recording sheet 120.
The recording sheet 120, the preceding direction of which has been adjusted, is conveyed to the recording area by being pinched by the sheet conveying roller 130 and the pinch roller 129 as shown in FIG. 16D. At this juncture, the driving gear 135 rotates in the direction indicated by an arrow S in FIG. 16D. Therefore, the planetary arm 140 is given moment in the direction indicated by an arrow T in FIG. 16D so that the planetary gear 139 parts from the sheet feeding shaft gear 119. The structure is thus arranged so as not transmit driving power from the driving source to the sheet-feeding roller (not shown) when the nipping portion bits the recording sheet 120.
The structure of the conventional automatic sheet-feeding device described above has advantages such as to simplify the driving switching mechanism, and to control the automatic sheet-feeding device, among some others. However, only by the contact pressure of the separation roller to the sheet-feeding roller is used for generating the nip abutting force, which is needed for a recording medium to be bitten by the sheet-conveying roller. As a result, when the recording medium, which is comparatively thick or liable to slip, is fed, the abutting force becomes insufficient, and in some cases, it is disabled to bite such recording sheet into the nipping portion of the sheet-conveying roller.